This invention relates to a method and apparatus for adjusting axle parameters that affect axle speeds for a tandem drive axle so that an inter-axle differential is not required.
Tandem drive axles are typically used in heavy-duty truck applications. One example of a heavy-duty truck is a semi-tractor and trailer vehicle. The drivetrain for a semi-tractor typically includes a front non-drive steer axle and a tandem drive axle. A fifth wheel, positioned over the tandem drive axle, is used to connect the trailer to the tractor.
The tandem drive axle includes a front drive axle connected to a rear drive axle via a thru-shaft. An engine provides driving input to a center differential of the front drive axle via an input shaft. The thru-shaft couples the center differential of the front axle to a center differential of the rear drive axle to transfer driving torque from the front drive axle to the rear drive axle.
Under certain conditions, the front and rear drive axles may require speed differentiation. For example, speed differentiation is required in situations where axle loads are not distributed evenly between the front and rear drive axles or if tires on the axles have different rolling radii. To achieve speed differentiation, the front axle typically includes an inter-axle differential housed within the center differential. The inter-axle differential allows for speed differentiation between the front and rear drive axles. Incorporating an inter-axle differential into the tandem drive axle is expensive and adds additional weight to the vehicle.
Some specialty off-highway applications use tandem axles that do not include inter-axle differentials, allowing wheel slip to equalize axle speeds on paved surfaces. This increases tire wear, reduces axle component life, and reduces fuel economy, which is undesirable.
Thus, it is desirable to provide a tandem drive axle that does not require an inter-axle differential that overcomes the deficiencies discussed above.
A control system for a heavy duty vehicle is used to maintain pre-selected axle parameters at desired conditions so that axle differentiation for a tandem drive axle is not needed. A tandem drive axle includes a front drive axle connected to a rear drive axle with a thru-shaft. Axle parameters such as differences in tire rolling radii, unequal weight distribution between the front and rear drive axles, and a suspension set at an improper height (affecting oscillation inputs from drivelines) can affect axle speeds, thus necessitating axle differentiation.
The subject invention utilizes a control system that determines differences in tire rolling radii by monitoring wheel speed and/or tire pressure and adjusts tire pressure for the tires mounted to the front and rear axles to maintain each of the tires within a desirable tire rolling radii range or notifies an operator when such adjustment is unachievable and tire maintenance is required. The control system also generates control signals for adjusting weight distribution between the axles and for adjusting suspension height to maintain desired levels.
The axles include center differentials that distribute driving torque from an engine to driving wheels that support the tires. Brakes are mounted within the wheels to provide braking for the vehicle. An automatic traction control system controls axle speed via wheel braking or a center differential locking control is used to control axle speeds via the center differentials to maintain vehicle tractive effort capability.
The subject method and apparatus eliminate the need for an inter-axle differential mechanism resulting in improved fuel economy, weight reduction, and cost reduction. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.